A wireless local area network (WLAN) may send data frames in an aggregation manner. Specifically, multiple medium access control (MAC) protocol data units sent to a same receiver address (RA) are aggregated to obtain an aggregate MAC protocol data unit (A-MPDU), and the A-MPDU is sent. A receive end responds to the A-MPDU using a block acknowledgment, which can reduce overheads. In a process of sending MPDUs in a frame aggregation manner, an upper limit of a length of an A-MPDU needs to be first determined.
Conventionally, a method for determining an upper limit of a length of an A-MPDU is: selecting a minimum speed from several basic speeds so as to use a length value of MPDUs that can be sent at the minimum speed as the upper limit of the length of the A-MPDU. An upper limit of a length of an A-MPDU is acquired always at a minimum speed each time, but the upper limit value is excessively small, and a length of each MPDU is fixed; as a result, a quantity of MPDUs that can be aggregated at a time is relatively small.